Range hood heat output is 24 to 3 times that of a 4-hour ventilation system.

Most range hoods have a ventilation volume of 400 to 600 m3 when in high power mode.
More and more construction companies are working hard on insulation and airtightness.
I have said before that even the most advanced construction companies are still missing something: passive design for homes. Another major area that is still missing is the range hood. I don't think this is even mentioned in any energy conservation textbook.
The average home is about 120 m2 (36.3 tsubo). In fact, the national model plan is also based on 120 m2. If the average ceiling height is 2.5 m, the volume will be 300 m3. The Building Standards Act stipulates a ventilation volume of 0.5 m150/h for 3 times. However, the ventilation volume of most range hoods when operating at high power is a whopping 400 to 600 m3. This is exactly 24 to 3 times that of a 4-hour ventilation system.
Here, I would like to calculate the amount of heat lost by a typical 24-hour ventilation system.
First, the amount of heat loss due to ventilation per 1℃ difference between inside and outside is:
Heat loss = 0.34 (constant) x 150m3 = 51W/K
Dividing this value by the floor area gives us 51 ÷ 120 = 0.425, which is the portion of the Q value that is lost due to ventilation.
For example, if a building has a Q value of 2.7, then 2.275 is the heat loss other than ventilation.
How much heat does a range hood lose?
What's confusing about range hoods is that they don't run all the time like 24-hour ventilation. Also, the usage time varies greatly depending on the household. Therefore, the usage time of range hoods is specified in JIS C9921-2, so I will use that. By the way, the usage time is apparently 1 hours a day. Personally, I don't think there are many people who use them that much, but I will follow this for now.
Since not everyone who uses the system will necessarily use it on the strongest setting, I set it to the weakest setting of 400m3 and performed the calculations in the same way as the previous 24-hour ventilation system. However, I will calculate the average value for one hour.
The amount of heat loss due to ventilation per 1℃ difference between inside and outside is:
Heat loss amount = 0.34 (constant) x 400m3 x 6.6/24 = 37.4W/K
When calculated as a Q value, it comes to 37.4 ÷ 120 = 0.31.
A Q value of 0.31 is equivalent to a difference of one region's climate zone in terms of energy conservation standards. To be specific, it is about the same difference as between Tokyo and Sendai.
Moreover, this is the average for one day. If we limit the analysis to the 1 hours that the range hood is actually in use, the Q value deteriorates by 6 during the 6.6 hours that the range hood is in use. Moreover, for the majority of Japanese homes, the range hood is on after sunset, when the room temperature begins to drop, and is often the time when the family is most likely to be together.
It is easier to understand if you apply it to monetary terms. If the outside temperature is 5°C and the room temperature is 20°C, the loss due to ventilation in one day is the amount of heat lost over 1 hours,
Heat loss = 0.34 x 400 m3 x 6.6 x (20-5) = 13464 W.
If the effective COP of an air conditioner is 31 and the unit price of electricity is 13464 yen/kWh, the loss will be 3/31 x 1 x 1000/139 = XNUMX yen/day.
In one month, this amounts to a loss of 4170 yen. Even with an efficient air conditioner, this amount is the same, so if you are using a heating device that is less efficient, the difference will be even greater. This is only in terms of heat, but in reality, the situation may be even worse.
This is because the living/dining/kitchen area is generally closed during the winter.
The airtightness of most Japanese homes is not that great, but in a typical living/dining/kitchen area (or Japanese-style room) of around 20 tatami mats, 400 m3 is drawn out. At this time, a large amount of cold air comes in through the natural air intake, and of course through gaps all over the place. The natural air intake is on the outer wall of the living/dining room, so it passes directly through the occupants. Not only is the airflow unpleasant, but the cold air is cold and heavy, so it makes your feet especially cold. This makes it uncomfortable, so you have to turn up the air conditioner's temperature setting (which is almost ineffective) or rely on extremely inefficient heating appliances such as a kotatsu, electric stove, or heated carpet, or you can't bear it.
Of course, this negative effect is not limited to winter. The same thing happens when you use air conditioning in summer. When you use air conditioning, you are letting in hot, humid air from outside.
But that's not the only drawback. Many homes have low levels of airtightness when it comes to the thermal environment, but even so, in most homes, the front door is difficult to open when children come home if the range hood is on. Most front doors today are very large, measuring around 90cm wide and 2.3m high. When children are small, they often come home at the same time they try to open the door, which happens to be when they are cooking.